INDEX reaction coefficients

The final group is for reaction data. They are indexed by the registry numbers for reactants and products, and then the reference key. The reaction coefficients are also included in the indices. 

The susceptibility or mixing coefficients, pj and pj , depend upon the position of the substituent (indicated by the index, /) with respect to the reaction (or detector) center, the nature of the measurement at this center, and the conditions of solvent and temperature. It has been held that the p/scale of polar effects has wide general applicability (4), holding for substituents bonded to an sp or sp carbon atom (5) and, perhaps, to other elements (6). The or scale, however, has been thought to be more narrowly defined (7), holding with precision only for systems of analogous pi electronic frameworks (i.e., having a dependence on reaction type and conditions, as well as on position of substitution). 

The detailed model was constructed as described by Carslaw et al. (1999, 2002). Briefly, measurements of NMHCs, CO and CH4 were used to define a reactivity index with OH, in order to determine which NMHCs, along with CO and CH4, to include in the overall mechanism. The product of the concentration of each hydrocarbon (and CO) measured on each day during the campaign and its rate coefficient for the reaction with OH was calculated. All NMHCs that are responsible for at least 0.1% of the OH loss due to total hydrocarbons and CO on any day during the campaign are included in the mechanism (Table 2). Reactions of OH with the secondary species formed in the hydrocarbon oxidation processes, as well as oxidation by the nitrate radical (NO3) and ozone are also included in the... 

The bulk polymerization of acrylonitrile in this range of temperatures exhibits kinetic features very similar to those observed with acrylic acid (cf. Table I). The very low over-all activation energies (11.3 and 12.5 Kj.mole-l) found in both systems suggest a high temperature coefficient for the termination step such as would be expected for a diffusion controlled bimolecular reaction involving two polymeric radicals. It follows that for these systems, in which radicals disappear rapidly and where the post-polymerization is strongly reduced, the concepts of nonsteady-state and of occluded polymer chains can hardly explain the observed auto-acceleration. Hence the auto-acceleration of acrylonitrile which persists above 60°C and exhibits the same "autoacceleration index" as at lower temperatures has to be accounted for by another cause. 

Ihrig and Smith extended their study by running a regression analysis including reaction field terms, dispersion terms and various combinations of the solvent refractive index and dielectric constant. The best least squares fit between VF F and solvent parameters was found with a linear function of the reaction field term and the dispersion term. The reaction field term was found to be approximately three times as important as the dispersion term and the coefficients of the terms were opposite in sign. 

The transfer coefficient a is generally an index indicative of the symmetry of the energy barrier for a redox half-reaction. The significance of this definition is the following. 

Solutions of isolated dioxiranes, characteristically dimethyldioxirane (DMD) in acetone, possess a pale yellow color, which serves as a convenient analytical index for monitoring the dioxirane consumption in oxidation reactions and kinetic studies. For DMD, the absorption maximum (n-jt transition ) centers at ca 325 nm, with a molar extinction coefficient (e) of 12.5 0.5 M cm in acetone. The alternative and more rigorous analytical method for dioxirane quantification utilizes iodometry (Kl/starch). 

Equation 9.72 introduces a great deal of nomenclature at once. Chemical species are indexed by k, with K being the total number of species (later, when we generalize the kinetics to multiple phases, the variable Kg is used for the number of gas-phase species) reactions are indexed by the variable i, with / being the total number of reactions in the mechanism the name of species k is represented by X v ki is the stoichiometric coefficient of species k in the forward direction of reaction i is the stoichiometric coefficient of species k in the reverse direction of reaction i. 

Here c(x, t)dx is the concentration of material with index in the slice (x, x + dx) whose rate constant is k(x) K(x, z) describes the interaction of the species. The authors obtain some striking results for uniform systems, as they call those for which K is independent of x (Astarita and Ocone, 1988 Astarita, 1989). Their second-order reaction would imply that each slice reacted with every other, K being a stoichiometric coefficient function. Only if K = S(z -x) would we have a continuum of independent parallel second-order reactions. In spite of the physical objections, the mathematical challenge of setting this up properly remains. Ho and Aris (1987) have shown how not to do it. Astarita and Ocone have shown how to do something a little different and probably more sensible physically. We shall see that it can be done quite generally by having a double-indexed mixture with parallel first-order reactions. The first-order kinetics ensures the individuality of the reactions and the distribution... 

Quantitative relationships have been reported between the global electrophilicity index and the experimental rate coefficients for the reactions of thiolcarbonates and dithio-carbonates with piperidine. The validated scale of electrophilicity was then used to rationalize the reaction mechanisms of these systems. This scale also makes it possible to predict both rate coefficients and Hammett substituent constants for a series of systems that have not been experimentally evaluated to date.48... 

A global electrophilicity index of common benzylating and acylating agents has been established from MO calculations and it shows a quantitative linear correlation with the experimental substrate selectivity index from a series of benzylation and acylation reactions.21 The values of relative rate coefficients predicted from the index may be accurate to within 10%. The reaction of /-butyl chloride with anisole catalysed by /Moluenesulfonic acid in supercritical difluoromethane has been subject to kinetic analysis.22 The proportions of substitution at the ortho -position and disubstitution increase at lower pressures, attributed to the decrease in the hydrogen-bonding ability of the solvent. 

Transport and Transformation of Chemicals A Perspective. - Transport Processes in Air. - Solubility, Partition Coefficients, Volatility, and Evaporation Rates. - Adsorption Processes in Soil. - Sedimentation Processes in the Sea. - Chemical and Photo Oxidatioa - Atmospheric Photochemistry. -Photochemistry at Surfaces and Interphases. -Microbial Metabolism. - Plant Uptake, Transport and Metabolism. - Metabolism and Distribution by Aquatic Animals. - Laboratory Microecosystems. - Reaction Types in the Environment. -Subject Index. 

It may not be appropriate to consider the scattering coefficient to be constant, and this point may become important in evaluation of trends monitored during a catalytic reaction experiment. Kortiim et al. (1963) pointed out that the scattering behavior depends on the ratio of refractive indices of the sample and the surrounding medium. As an example for a change in the refractive index of the sample, Kortiim described the adsorption of water, which reduces the scattering coefficient. Hence F(p) will increase, which could erroneously be interpreted as an increase in absorption. 

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